Field of the Invention (Technical Field): Embodiments of the present invention relate to the general field of electrosurgical generators that are used to power devices, such as instrument probes, and instrument probes developed for use in surgical and medical procedures.
The use of electrosurgical instruments in various types of surgical procedures has become widespread and generally consists of a system whereby a treatment device probe is connected to an electrosurgical generator. The device probe delivers the energy from the electrosurgical generator to the tissue treatment site via electrodes to provide a therapeutic effect. Device probe and electrosurgical generator architecture have been developed for particular therapeutic needs, depending upon, for example, the goals of treatment, the tissue type to be treated, and the treatment environment. Most commonly, electrosurgical generators consist of either monopolar or bipolar configurations, or both, which have become well known in the art. Likewise, either monopolar or bipolar treatment device probes have been developed to connect to those types of electrosurgical generators via a dedicated electrosurgical generator output port, either monopolar or bipolar, respectively. Active (or working) and return (reference) electrodes then function in a variety of ways based upon, for example, configuration, architecture, and connection to the electrosurgical generator. In this manner, either a monopolar or bipolar output portal, or both, exists on the electrosurgical generator into which the device probe, either a monopolar or bipolar device respectively, is connected. A monopolar device is connected to a monopolar output portal on the electrosurgical generator and, likewise, a bipolar device is connected to a bipolar output portal on the electrosurgical generator. Typically, feedback from the treatment site is then managed by way of the relevant monopolar or bipolar circuitry within the electrosurgical generator and between the device probe electrodes that are connected to the electrosurgical generator accordingly.
More generally, and to date, the electrosurgical industry has provided a wide variety of products that rely upon the importance of bulk property measurement of in situ structures/components for determining the extent and effect of electrosurgery, which has been well documented. Quantifying energy input indirectly through temperature measurement, fluid field impedance measurement, and fluid field capacitance measurement is believed to effectively correlate the degree to which electrosurgery will effect tissue and the host response thereof. Since such correlations have been extremely inconsistent in practice, a significant amount of confusion has surfaced regarding the validity and accuracy of therapeutic electrosurgical protocols, often leading to the reduction in use of electrosurgical devices for certain applications.
Historical evolution of the prior art has been to provide specific output portals for the most common types of electrosurgery; those being monopolar and bipolar. Each of these output portals is designed to provide specific controls that limit the amount of maximum current, voltage or time-based modulations of current and voltage in response to the variations in factors at the treatment site. The result is intended to control the overall output to the active (working) end of the attached device probe and keep its general state of operation within an arbitrarily selected specified “safe-range” to avoid excessive heat, current, or current density from forming within the surgical site or elsewhere within the patient at the time of treatment. Because of this prior art, the sensing devices at the tip of the probes are limited in their sensing modalities as they relate to these two modes of power output (both Monopolar and bipolar), namely temperature measurement, fluid field impedance measurement, and fluid field capacitance measurement are used to govern power delivery to the probes.
Such circuitry for this monopolar or bipolar configured output portals is contained within the physical confines of the electrosurgical generator enclosure itself, proximal to the connection of the device probe, and is coupled to an electronic and software controller that monitors said variables and continually checks their time-varying values against preset performance limits. When these performance limits are exceeded, the controlling algorithm forces a safety trip, thus modulating or shutting down the primary radio frequency-power output to the working end of the attached device. The specifics of these predefined software controlled trip points is that they are based on the electrophysical constraints electrosurgical generator manufacturers have placed on the output portals, which as previously discussed, are configuration specific (monopolar or bipolar). Thus, the physical spacing of primary components such as the active (working) and return (reference) electrodes plays a paramount role in the variation of those specific characteristics that govern said trip points for safety control. The overall industry result from this configuration model is a trajectory of “silo” thinking for each specific electrosurgical output portal, meaning that devices have been optimized for either the monopolar output portal or bipolar output portal of electrosurgical generators. Traditional thinking, based on the prior art, has been that there is no advantage in modifying the traditional physical spacing of components typically assigned to any specific output port for any specific mode, meaning that a monopolar procedure that involves a separated ground pad, typically placed at a great distance from the surgical site, has been thought to need such separation to operate effectively. Furthermore, such separation is exactly why the procedure has been named “mono” polar as the electrical poles are separated by such large relative distances that only a single pole is effectively at work within the surgical site. On the other end of the spectrum is the “bi” polar method of electrosurgery which has drawn its name from the physical basis of active (working) and return (reference) electrode proximities to one another. Thus, to date, the industry has remained ensconced in fixed paradigm of one treatment device probe configuration per output port of the electrosurgical generator; i.e. monopolar device to monopolar output port and bipolar device to bipolar output port.
U.S. Pat. Nos. 6,214,003 and 6,461,352, to Morgan, describes a fluid flow through channel that provides the ability for a fluid at the surgical site to flow through both the insulator and the electrode. In that application, the invention provides the flow through channel in the insulator and electrode because the invention seeks to remove things from the active/working electrode so that it can work better in that system. That invention therefore seeks to remove things, like bubbles so that the electrode can re-wet and continue working and effectively without obstruction, thereby enhancing visualization at the surgical site. While that invention may enhance visualization, it does not recognize the advantages of bringing all the elements within the treatment site together so that a reaction therebetween can occur.
U.S. Pat. No. 6,890,332 to Truckai, describes a fixed electrode in a recessed portion of the tip. The tip of that device, however, does not provide protection from the active electrode coming into contact with tissue at a surgical site. This is because the slight recession at the tip does not continue to provide protection from contact with the active electrode when the tip is pushed directly into the tissue. Instead, the tissue merely deforms slightly, thereby allowing the tissue to extend into the slight recession of the tip and thus make contact with the active electrode. Because the impedance value of tissue is different from that of the fluid in the surgical site, each time that the active electrode makes and breaks contact with the tissue, the impedance seen by the electrosurgical generator suddenly changes thereby making it difficult or impossible to adequately regulate the power delivered to the tip of the electrosurgical probe. Furthermore, this is why impedance, capacitance, and even to an extent temperature have been the primary parameters that have been used to control energy output from the electrosurgical generator as described above. This method of regulation of the electrosurgical energy output is extremely inaccurate when placed in a setting where tissue preservation or limited collateral damage is desired because it is often recommended that the user/physician manually induce contact of the active (working) electrode to the tissue in a non-controlled (relative to all users/physicians) manner that then continually alters the impedance, capacitance, sand temperature, the bulk properties, at the treatment site. This leads to a deficit in the ability of the user/physician to effectively control energy deposition and transfer to the treatment site in a method that preserves tissue and prevents collateral damage.
Prior art devices have addressed the problem of continually varying target tissue site impedance through increasingly complex software algorithms that monitor peak voltage outputs from the ESU using rapid circuit sensing and triggering, thereby limiting the output power as the voltage spikes to prevent excessive energy deposition to target tissue sites. These algorithms add significant complexity to ESU monitoring software algorithms and their corresponding validation. Furthermore, in many instances even with rapid peak voltage throttling by software, the total energy output from active electrodes touching tissue remains excessive to prevent significant amounts of necrosis and collateral damage as evidenced by the current literature on the topic.
Additionally, dealing with the large Voltage Standing Wave Ratios (VSWR's) created by these intermittent contacting electrode designs during electrosurgical processes often necessitates use of high-heat bearing signal generating components within the ESU (electrosurgical generator) to provide sufficient stability of the output signal against these reflections. The combined resistive, capacitive, inductive, and reflected impedance can be seen from above as accretive toward the total impedance and thereby produce much greater amounts of heat within the source (ESU). Common examples of such electrical components that must be sized to handle these types of loads include Field Effect Transistors (FET's), Operational amplifiers (Op-Amps), and inductors. The overall size of ESU's is often dictated by the requirements of heat dissipation within the console so as not to yield an excessive external skin temperature on the exterior of the housing.
Thus there is a need for device designs that protect the active (working) electrode from tissue contact and thereby stabilize the primary variables at work in causing fluctuations in load impedance at the surgical site, thus affording ESU designers greater simplicity in construction of hardware/software combinations and in some cases the complete elimination of software, such that “state-machine” electronic logic may be used which is constructed of purely hardware components that can be used to manage the lower VSWR's that are now part of protected electrode operations.
There is thus a need for an electrosurgical probe which houses the active electrode within a protected plenum that prevents contact of the active electrode with tissue, while allowing fluid at the electrosurgical site to make contact with the active electrode, and while simultaneously partially containing gasses created by the electrosurgical process such that they react with one another rather than in a manner that removes the products of electrosurgery away from the treatment site. Additionally, this plenum can then be used as a mechanical implement.
Surgical devices that deploy an electrical circuit between electrodes do so in an electrically conductive medium, which may be either in vivo biologic tissues or delivered media such as electrolyte solutions. The tissue effects produced by these devices are dependent upon the events occurring at or around the electrodes as electrical energy is converted to therapeutically useful forms. Converted energy forms can be either near-field at the electrode surface or far-field projected away from the electrodes. Near-field effects are produced by electrical current and include physiochemical events like electrothermal and electrochemical conversions; far-field effects are produced by electromagnetic radiation forces like magnetic flux densities, voltage potentials, or displacement currents generated around the electrodes. Gross electrical conduction in biological tissues is principally due to the conductivity of in situ interstitial fluids which are electrolyte water-based and thus predominantly ionic. Since the electrical charge carriers in metal electrodes are primarily electrons, the transition between electronic and ionic conduction is governed by physiochemical processes at the electrode-to-water interface within the conductive media, even though this process can be altered by electrode contact with macromolecular biologic material. Electrically conductive solutions have been used for many decades to complete surgical device circuits and no longer alone serve as a proprietary method of circuit completion. Water is the common operational media for both direct current and alternating current formulations that have been deployed in surgical device designs.
Surgical use of direct current induces tissue necrosis as a means to destroy unwanted tissue through near-field electrical current effects delivered into biologic structures. Electrolytic ablation, or tissue electrolysis, is a technique which consists of placing an anode electrode and cathode electrode at various points within or adjacent to tissue and driving direct current which typically has a range of about 40 mA to about 100 mA between them and through the biologic mass to induce tissue electrolysis. The products of tissue electrolysis kill cells by creating, in a spherical area surrounding the each electrode, local changes within tissue pH too large for cells to survive. These pH changes are created by toxic products such as chlorine, oxygen, and hydrogen ions at the anode electrode and hydrogen gas and sodium hydroxide at the cathode electrode. The region surrounding the anode becomes very acidic (˜pH 2) and surrounding the cathode becomes strongly alkaline (˜pH 12) with the amount of necrosis dependent upon the total electrolysis dose measured in coulombs as a product of tissue current delivery and time. A pH less than 6.0 at the anode and greater than 9.0 at the cathode reflects total cellular necrosis. Direct current applications deliver static electromagnetic fields that have inconsequential energy quanta in the region of non-necrotic tissue. Electrolytic ablation does not rely upon a thermal effect as tissue temperatures rise minimally during these procedures to levels not associated with cell death.
Surgical use of alternating current has been designed to induce therapeutic necrosis for volumetric tissue removal, coagulation, or dissection through near-field electrical current effects within biologic tissues. Radiofrequency wavelengths and frequencies do not directly stimulate nerve or muscle tissue; and, so are prevalent in medical applications. Radiofrequency surgical devices utilize tissue as the primary medium like in direct current applications; however, these surgical devices produce resistive tissue heating (ohmic or Joule heating) by an alternating current induced increase in molecular kinetic or vibrational energy to create thermal necrosis. In order to obtain the desired levels of thermal necrosis through resistive heating in a media with the exceptionally large specific heat capacity of water found in and around biologic tissues, high-levels of alternating current deposition are required to maintain heat production and conduction to remote tissue in the presence of treatment site thermal convection. In certain settings, high-level energy radiofrequency devices can be configured to produce water vapor preferentially through very rapid and intense resistive heating, overcoming the high heat of vaporization at the treatment site. Coincident with this method, the far-field time-varying electromagnetic forces of these devices deliver energy quanta able to generate charged plasma particles within the water vapor cloud. This ionizing electromagnetic radiation can induce an electron cascade, which operates over very short distances (Debye sphere) and with electron temperatures of several thousand degrees Celsius, to produce therapeutic molecular disintegration of biologic tissues as its action decays into heat. Radiofrequency thermal ablation and plasma-based techniques display use limitations associated with their design. Thermal and plasma lesions spread according to induced gradients; but, because of the variable energy transfer coefficients in the treatment settings of biologic tissues, iatrogenic tissue charring, necrosis, and collateral damage from imprecise heating or excess energy deposition can occur.
Electrolytic ablation, radiofrequency thermal ablation, and radiofrequency plasma-based surgical devices are designed for a direct electrode-to-tissue interface, concentrating near-field electrical energy to perform surgical work centered upon therapeutic necrosis. Collateral damage is a normal procedural consequence since the application locales to which these devices are deployed can often accommodate an excess or imprecise application of energy to ensure expedient procedural efficacy within varying treatment site conditions. From a surgical work energy procurement standpoint, these procedures are defined by an inefficient use of electrical energy due to the excess energy deposition that occurs within biologic tissue producing iatrogenic collateral damage. Far-field electromagnetic forces, although present, are confounded by tissue current deposition or, in the case of plasma-based radiofrequency devices, are of such a high intensity constituting local ionizing electromagnetic radiation. Electrolytic ablation, radiofrequency thermal ablation, and radiofrequency plasma devices all struggle in balancing volumetric tissue removal with healthy tissue loss because of excess collateral energy deposition into tissue.
Newer surgical uses of alternating current include non-ablation radiofrequency systems which deliver low-level energy to tissues through a protective tip architecture that prevents active electrode-to-tissue contact and therefore do not rely upon a direct electrode-to-tissue interface. The devices are deployed in a saline immersion setting with the protected electrode creating a more controlled and directed energy delivery to modify or precondition tissue allowing tissue preservation even during resection or débridement applications. Because the electrodes do not contact tissue during activation, electrical current deposition is concentrated into an interfacing media within the protective housing rather than directly into and through biologic tissue as in ablation-based devices. The protective housing provides the ability to move, manipulate, and segregate the near-field effects both tangentially and perpendicularly to the tissue surface during modification or preconditioning; and, it can serve as a mechanical implement and selective throttling vent/plenum during use. For example, the near-field effects are often configured to match current density dispersion with biologic tissue surfaces in a procedure-specific manner. This design allows more consistent electrical current near-field effects at the electrode surface because the circuit is not required to accommodate widely fluctuating impedance changes that tissue contacting electrodes create. Accordingly, tissue electrolysis and resistive (ohmic or Joule) tissue heating can be prevented. These devices allow a more efficient surgical work energy procurement as iatrogenic collateral tissue damage is minimized without compromising procedural efficacy. Non-ablation devices can deliver useable far-field electromagnetic forces to surface and subsurface tissues designed to create quantitatively and qualitatively larger strengths in tissue not damaged by excessive current deposition or ionizing electromagnetic radiation. These devices are used to permit normal tissue healing responses during modification and preconditioning through segregated near-field effects, while creating far-field electromagnetic intensities designed to induce tissue healing responses within the preserved tissue not subjected to collateral damage.
The application of radiofrequency energy upon an electrically conductive media can follow distinct pathways based upon the nature of electrical work desired. These pathways are determined by structural rearrangements of water molecules that are subjected to the radiofrequency energy effects upon the interfacing media molecular dynamics. Whether the interfacing media is in or around biologic tissues, it is governed by hydrogen bond behavior and proton transport that allow for widely malleable structural fluctuations of liquid water molecules. These fluctuations are due to water's very dynamic hydrogen bond network which displays the inherent ability to both exhibit simultaneous behavioral states and to rapidly reconfigure to accommodate physiochemical perturbations. With ablation- and plasma-based radiofrequency systems, resistive heating is produced predominantly by molecular kinetic and vibrational motions occurring within and amongst the hydrogen bond network. Rapid and intense resistive heating can produce a phase transition from liquid water to water vapor as vibrational motions further exert a predominate role in the ultrafast loss of liquid water's structural configuration leading toward phase transition. This process is energy intensive due the high specific heat capacity and heat of vaporization of water. In the presence of charged species like salts, this temperature driven phase transition process from rapid resistive heating at the electrode is slowed by 3-4 times, which further increases the amount of energy required to reach phase transition. Once phase transition occurs, water vapor can be ionized by the electromagnetic forces associated with this radiofrequency energy level required to drive the heating process to phase transition.
In contrast, non-ablation radiofrequency energy requirements are low because the requisite energy input is limited to splitting water which then creates a repetitive molecular energy conversion loop that self-fuels due to the exothermic reaction of water reconstitution. Charged species like salts, in distinction to their effect during resistive heating, decrease the system energy requirements because they serve as a energy salt-bridge catalyst facilitating water splitting by forming, breaking, and nucleating hydrogen bonds between acid-base pairs and water molecules. As this study demonstrates, water splitting is a low energy initiation process associated with non-ionizing electromagnetic forces. Without the protective housing around the active electrode, this physiochemical process would be rendered inconsequential due to the large fluid flow and convective forces present during surgical application. It is for this reason that ablation-based systems have been designed with ever increasing energy levels and associated ionizing electromagnetic radiation while non-ablation systems have focused upon limiting energy requirements by refining the energy procurement and delivery process to preserve tissue.
The near-field electrothermal effects of non-ablation radiofrequency energy are governed by the nature of electrical work performed upon the intermolecular hydrogen bonds of water-based interfacing media. Energy generation is created by a repetitive molecular energy conversion loop rather than by high energy resistive heating of water. Splitting water is a mildly endothermic reaction that is driven by the low-energy near-field effects of non-ablation current; whereas, reconstitution back to water is exothermic providing assistive energy for further repetitive molecular energy conversion loops ultimately deployed for surgical work. The alternating current allows each electrode to perform each redox half-reaction, but the effects can vary between electrodes because of architectural nuances. The initial reaction activation barrier is the four electron oxidation of water to oxygen during the anode phase of water splitting. This barrier is overcome by increased voltage potentials between the electrodes rather than by increased current so that architectural nuances of the electrodes are primarily due to the magnitude of voltage potential difference rather than current density disparities. At the frequencies employed, this process is very inefficient at producing non-soluble gas. When non-soluble gas is produced, it is limited to molecular hydrogen and oxygen which is effectively managed by the protective housing throttling vent/plenum. Water vapor is not produced demonstrating the low-level energy deployment well below water's heat of vaporization. As a corollary, excessive water vapor production during resistive heating has been shown to significantly impair visualization of the ablation treatment site.
The near-field electrochemical events of non-ablation radiofrequency energy are also governed by the nature of electrical work performed upon the water-based interfacing media. During the repetitive molecular energy conversion loop, alternating current can also facilitate an otherwise inefficient and more complex chemical reaction within the interfacing media rather than simple phase transition to water vapor as in ablation-based devices. The intermediary products and reactants of the repetitive molecular energy conversion loop may combine to create an acid-base shift desirable for therapeutic interventions through techniques such as capacitive deionization and concentration enrichment. Because of the protective housing throttling vent/plenum, these products can be delivered in a controlled and localized fashion through precipitation, sedimentation, thermal, or chemical gradient forces into the treatment site through redox magnetohydrodynamic fluid flow. Much like the electrothermal gradients, these electrochemical modification gradients can be driven toward tissue surfaces. For example, sodium hypochlorite can be precipitated preferentially based upon device design configuration to react with a wide variety of biomolecules including nucleic acids, fatty acid groups, cholesterol, and proteins at tissue surfaces. Additionally, pH shifts have been shown to produce tissue surface alterations effecting transport properties and extracellular composition. Water vapor itself is not a therapeutic product or event, limiting ablation-based devices to thermal interventions.
The far-field effects of non-ablation radiofrequency devices can manifest due to a minimal current density at or within biologic tissues, and hence magnetic field flux densities within the protective housing, and an high voltage potential force resulting in non-ionizing electromagnetic intensities designed for therapeutic use. Not only do these high voltage potentials increase the ability to perform redox reactions in conductive media by facilitating the repetitive molecular energy conversion loop, voltage potentials not coincidentally have been shown to be a principle driver of non-ionizing electromagnetic effects upon biologic tissue. Because these electromagnetic forces carry energy that can be imparted to biologic tissue with which it interacts, higher voltage potentials enable oxidization or reduction of energetically more demanding tissue constituent macromolecular compounds other than water. These forces are deployed at the protective housing-to-tissue interface, unencumbered by current deposition, typically scaled at about 0.1 to about 1.5 mm distances from the electrode, rather than processes at the electrode-to-tissue interface as in, for example, plasma-based systems where the ionizing electromagnetic radiation generates high energy thermal particles that interact with biologic tissue.
Once non-ionizing electromagnetic fields have been produced from a given charge distribution, other charged objects within the field, such as biologic tissue, will experience a force, creating a dynamic entity that causes other tissue charges and currents to move as their strengths are typically lower. When non-ionizing electromagnetic radiation is incident on biologic tissue, it may produce mild thermal and/or weaker non-thermal field effects. Complex biological consequences of these fields are exerted through such mechanisms as tissue voltage sensor domains, stress response gene expression, and direct voltage-to-force energy conversion molecular motors.
Further, Chondron density within the Superficial Zone has been shown to decrease with age, disease, injury, and in response to some interventions and may predispose articular cartilage to extracellular matrix-based failure through an inability to support the mechanotransductive demands of physiologic loading. Since chondron shape and orientation reflect inter-territorial extracellular matrix architecture, chondron density is an important descriptor for functional cartilage. Interventions that alter chondron density may provide insight into the treatment outcome of focal lesions.
Articular cartilage disease constitutes a large burden for our population which needs to be addressed with practical socioeconomic solutions. Because articular cartilage has offered surface changes as the first readily diagnosable visual and tactile cue of its degeneration, the orthopedic surgeon has been given the responsibility of first responder. This responsibility has led to the limited adoption of mechanical shavers and thermal or plasma ablation devices as a viable treatment for early articular cartilage disease due to the collateral damage and lesion progression they can cause. The opportunity to achieve successful early surgical intervention for articular cartilage lesions rather than waiting for full-thickness lesions to develop has recently been made possible with the advent of non-ablation radiofrequency technology.
Non-ablation radiofrequency technology enables the selective targeting and removal of the damaged tissue associated with early articular cartilage disease without causing necrosis in the contiguous cartilage tissue surrounding the lesion. This is accomplished by a protected electrode architecture (see FIG. 11) that prohibits electrode-to-tissue contact so that the resistive tissue heating and tissue electrolysis induced by electrical current and associated with tissue necrosis do not occur like in thermal and plasma ablation devices. The protective housing creates a primary reaction zone that is shielded from the large physical fluid-flow and convective forces present during surgical application enabling deployment of low-level radiofrequency energy to create low-energy physiochemical conversions that can be used for surgical work. A repetitive molecular energy conversion loop under non-ionizing electromagnetic forces is created wherein the rapid splitting and reconstitution of the water molecule occurs. A sister technology to the fuel cell that harnesses energy from the molecular bonds of water, these physiochemical conversions create products that are concentrated through techniques such as capacitive deionization and concentration enrichment and delivered to the treatment site in a controlled and localized fashion through precipitation, sedimentation, thermal, or chemical gradient forces via redox magnetohydrodynamic fluid flow. Thermal and plasma ablation devices have exposed electrodes making any attempt at low-energy physiochemical conversions inconsequential due to the large physical fluid-flow and convective forces present during surgical application; hence, their design necessitates a large amount of energy delivery to the treatment site that leads to collateral damage around the tissue target.
Non-ablation radiofrequency treatments are a surface-based intervention useful for surface-based conditions such as early articular cartilage damage. The low-level energy delivery is configured to modify/precondition diseased articular cartilage to a state amenable to a safe and effective gentle mechanical debridement with the protective housing leading edge. The non-ablation radiofrequency energy products effect the accessible and degenerate surface matrix structure of damaged cartilage tissue preferentially rather than the intact chondron and matrix tissue deep to the surface lesion level. In this manner, the non-ablation energy takes advantage of the altered pericellular and extracellular matrices of diseased cartilage by preparing damaged tissue for subsequent debridement with the protective housing leading edge through augmented and/or naturally facile tissue cleavage patterns. As early articular cartilage disease manifests as matrix failure, non-ablation radiofrequency technology creates a matrix-failure-based intervention that corresponds to cartilage biology.
The matrix failure of surface fibrillation remains an attractive therapeutic target for early surgical intervention modalities. By safely removing diseased surface fibrillation that serves as both a mechanical stress riser and a source of biologic load that propagate damage, these lesions can be stabilized. Lesion stabilization remains a necessary prerequisite toward articular cartilage tissue preservation since a residually healthy lesion site is an essential substrate for permitting or inducting effective healing responses. It has been demonstrated (see FIGS. 21A and B) that Superficial Zone characteristics with viable chondrocytes can be preserved during the targeted removal of surface fibrillation. Since the area adjacent to surface fibrillation often exhibits a soft character as noted by tactile cues, it would be useful if this tissue could be treated concurrent with the surface fibrillation whereby such a procedure would serve both as a therapeutic intervention for the tactile soft lesion and as a defined safety margin during the targeting of surface fibrillation lesions.
Chondron density has been shown to decrease with age, disease, injury, and in response to some interventions and may predispose articular cartilage to extracellular matrix-based failure through an inability to support the mechanotransductive demands of physiologic loading. Since chondron shape and orientation reflect inter-territorial extracellular matrix architecture, chondron density is an important descriptor for functional and degenerating cartilage. Interventions that alter chondron density through matrix modification may provide insight into the treatment outcome of focal lesions. It has previously been shown (see FIGS. 21A and B) that chondron density with live chondrocytes preferentially increases within the residual Superficial Zone after targeted removal of surface fibrillation with non-ablation radiofrequency techniques.
Aside from exploiting the mechanical cleavage patterns inherent in the Superficial Zone of early disease for lesion stabilization, theoretical matrix modification of the Superficial Zone without damage to the chondrocyte and chondron has been considered possible due to this zone's unique matrix properties. Articular chondrocytes are surrounded by a protective layer, the pericellular matrix (PCM), which is thought to function as a non-linear mechanical filter that modulates the physiochemical and biomechanical environments experienced by chondrocytes through processes like transmembrane signaling. The PCM displays distinct biomechanical properties when compared to the ECM. For example, the Young's modulus of the PCM is uniform with tissue depth in that it is similar to the ECM modulus of the Superficial Zone but significantly lower than the ECM modulus of the Transitional and Deep Zones. This disparity in properties, or stiffness ratio, allows the chondrocyte environment to be more consistent when confronted with large incongruities in local zone- and region-specific ECM forces. The PCM may protect the micromechanical environment of the chondrocyte in regions of high local strain such as in the Superficial Zone and may amplify lower magnitudes of local strain such as those occurring in the Transitional Zone. Further, the fluid permeability of PCM relative to the ECM is much lower allowing the functional phasic properties of the ECM during loading to be shielded from the chondrocyte. These unique properties would allow the chondron and chondrocyte in the Superficial Zone to accommodate alterations in the ECM with a protective PCM posture; whereas once the Transitional Zone chondron and chondrocyte are exposed to a surface-level environment due to acute damage or disease, the PCM of the Transitional Zone may amplify the increased ECM strains witnessed by the Transitional Zone's new surface locale to a detrimental level for both the chondrocyte and matrix. These PCM properties may partially explain the retention of viable chondrocytes in the Superficial Zone after non-ablation radiofrequency energy application; as well as, the significant disease progression that can be induced by mechanical shavers and thermal or plasma ablation devices that create an exposed and damaged Transitional Zone that is then subjected to repetitive physiologic loading.